Space Station crewmembers marked their 100th day in space Friday, ending a workweek focused on preparations for their first spacewalk, planned for Wednesday, Jan. 26.

Expedition 10 Commander and NASA ISS Science Officer Leroy Chiao and Flight Engineer Salizhan Sharipov are scheduled to leave the Pirs Docking Compartment airlock at 1:25 a.m. CST. Most of their spacewalk tasks involve outfitting the outside of the Zvezda Service Module.

They will install a work platform, mount a robotics experiment, check vents on systems that help control the Stationís atmosphere and install a scientific experiment.

After completing the work outside Zvezda, they will move back to Pirs. There, outside the docking compartment, they will install an experiment that examines the impact of spaceflight on microorganisms. They are expected to re-enter Pirs and close the hatch about 7 a.m.

Sharipov and Chiao completed one spacewalk prerequisite Friday morning. Both did the required cardiovascular evaluation exercise using one of the Stationís bicycle-like devices. They also did leak, valve and pressure checks on their Orlan spacesuits and the Orlan interface units in Pirs, completed suit communications checks and did a review of the spacewalk plan with flight controllers in Moscow.

Spacewalk activity earlier in the week included spacesuit battery charging beginning Tuesday, as well as preparation of spacewalk hardware and tools that day. They spent three hours staging equipment and tools on Wednesday, and on Thursday they activated and tested the suits.

Both suits will have red stripes. Chiao will be distinguishable by the U.S. flag on his shoulder.

The spacewalk will be broadcast live on NASA Television, beginning at midnight. CST Jan. 26. Coverage will continue through the end of the spacewalk.

In other activities during the past week, flight controllers on Jan. 15 raised the Stationís altitude by about 5.5 statute miles in a 20-minute reboost using engines of the ISS Progress 16 cargo craft docked at the rear of Zvezda. That was done to put the Station in the proper orbit for the arrival of ISS Progress 17 spacecraft, scheduled for launch Feb. 28 and docking March 2.

For much of the week, flight controllers conducted vibration and current tests on one of the 600-pound control moment gyros (CMGs) that control the orientation of the Station in space. The CMGs normally operate at 6,600 rpms, but can be operated at 15 other speeds. The test involved running CMG 2 at each of those speeds for four hours.

The CMGs use solar power. Three of the four on board are functioning, though the Stationís attitude could be controlled with two. The CMG which failed in mid-2002 is to be replaced on the next Shuttle mission.

For more on NASA, the crew's activities aboard the Space Station, future launch dates and Station sighting opportunities from anywhere on the Earth, visit:

www.nasa.gov

The next International Space Station Status report will be issued Wednesday, Jan. 26, after the spacewalk or earlier if events warrant.

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